This invention relates to a room audio speaker system.
As is well known, direct radiator loudspeaker devices are extremely inefficient in transforming the power input to the loudspeaker (electrical watts) into acoustic power (acoustical watts). Typically, for conventional direct radiator loudspeaker systems with enclosures of approximately three cubic feet in volume or less, the efficiency is only about 1 percent. These low efficiencies are the result of an impedance mismatch which results because the resistive component of the radiation load is very small in comparison with other impedances in the electroacoustical circuit. As is also well known, the resistive component (the radiation resistance) is inversely proportional to the effective radiation angle, in steradians, into which the loudspeaker device radiates. Indeed, the acoustic power radiated by a direct radiator loudspeaker system will double with each halving of the effective radiation angle for the system. Thus, if the loudspeaker diaphragm of such a system could be mounted flush with a wall surface in a room and at some distance from adjacent walls, the radiation angle would be reduced from 4.pi. steradians to 2.pi. steradians with a consequent doubling of the radiation resistance and of the relative acoustic power over that of such a system placed far from any such boundaries. It is clearly impractical, however, to require the recessing of all audio speaker equipment into room walls.
In a typical home audio system the loudspeakers will be placed adjacent a wall or other boundary surface of a room and in such a location that the impact of the room boundary surface upon the effective radiation angle of the loudspeaker will be a function of the frequency of the radiated sound. For the distances typically involved, the room boundary surface may serve to reduce the effective radiation angle for audio frequencies in the lower end of the audible range. For conventional low frequency direct radiator systems (i.e., woofers) the impact of the room boundary surface is found to extend over only a portion of the frequency range of the loudspeaker. This results in a frequency response curve in which the power radiated varies greatly with the frequency of the sound, even though the woofer may be capable of uniform power output working into an unvarying radiation resistance. This of course is an undesirable condition and it has long been a goal of designers to provide low frequency audio loudspeaker systems which have a flat frequency response curve.
In view of the foregoing it is a principle object of the present invention to provide a direct radiator loudspeaker system which has an improved frequency response curve, especially in the low frequency range of typical audio systems.
Equivalently, it is an object of the present invention to provide such a system in which, for such frequencies, the effective radiation angle of the loudspeaker system is substantially invariant as a function of frequency.